Four-component varifocal attachment for basic objective



July 22, 1969 MACHER 3,457,003

FOUR-COMPONENT VARIFOCAL ATTACHMENT FOR BASIC OBJECTIVE Filed June 29,1966 3 Sheets-Sheet 1 I ma 0'18 2 Kar/ Mac/7e! 5), glut R 5 AttorneyJuly 22, 1969 MACHER 3,457,003

FOUR-COMPONENT VARIFOCAL ATTACHMENT FOR BASIC OBJECTIVE Filed June 29,1966 5 Sheets-Sheet 2 Attorney y 22, 1969 I K. MACHER 3,457,003

FOUR-COMPONENT VARIFOCAL ATTACHMENT F? RASTC OBJECTIVE Filed June 29,1966 3 Sheets-Sheet :5

TABLE I TABLE I -rTr| vv|1 ||'|Ill[ 0 I00 m INVEN'IUR: Kar/ Mac/r8!Attorney United States Patent 01 3,457,003 Patented July 22, 1969 ice3,457,003 FOUR-COMPONENT VARIFOCAL ATTACHMENT FOR BASIC OBJECTIVE KarlMacher, Bad Kreuznach, Rhineland, Germany, as-

signor to Firma Jos. Schneider & Co., Bad Kreuznach, Rhineland, Germany,a corporation of Germany Filed June 29, 1966, Ser. No. 561,614 Claimspriority, applgcatign Germany, July 1, 1965,

c ,311 Int. Cl. G02b 15/00, 17/00, 9/34 US. Cl. 350-184 4 ClaimsABSTRACT OF THE DISCLOSURE My present invention relates to a varifocalobjective of the type wherein, e.g. as broadly disclosed in commonlyowned US. Patent No. 3,057,257, issued jointly to Giinter Klemt and me,and adjustable front group or varifocal attachment, consisting of twofixed positive components bracketing two axially movable negativecomponents, precedes an axially fixed rear group or basic objective,preferably also constituted by four air-spaced lens members. As appliedparticularly to the first component of the front group, the term fixeddoes not exclude a limited adjustability for focusing purposes, as iswell understood in the art.

In a commonly owned copending application filed by me jointly withRudolf Solisch and Walter Wtiltche, Ser. No. 366,878, dated May 12,1964, now Patent No. 3,273,457, there has been disclosed an objective ofthis type wherein the positive first component and the negative secondcomponent of the front group are each in the form of a doublet with aforwardly concave cemented surface of, respectively, negative andpositive refractivity; the other two components of this group aresinglets. This system is particularly suitable for use in reflex-typecameras, a refiex prism being accommodable (together with a diaphragm,if desired) in the space separating the two groups. The particularsystem disclosed in that copending application has a relative apertureof 121.8, a varifocal ratio (ratio of overall focal lengths f and f inthe two limiting positions of adjustment) of 1:4 and a mean focal lengthf (in an intermediate position of adjustment) approximately equal to thegroup focal length of the basic objective; if the mean overall focallength is assigned a value of 100 linear units (e.g., millimeters), thesystem has a back-focal length of numerical value 58.1 and a total axiallength of 522.93 units.

The general object of my present invention is to provide a more compactobjective system of this type, having substantially the same varifocalratio and relative aperture, which has a reduced axial length d and,with a back-focal length s equal to or greater than that of the priorsystem referred to, an increased ratio s'/d which is of value inmotion-picture and small photographic cameras since it simplifies theinstallation of shutters and other auxiliary elements behind the rearvertex. The invention also aims at realizing this improvement with smalllens diameters and maximum suppression of residual astigmatism fieldcurvature and coma.

The two doublets forming part of the front group of a system accordingto the present invention have confronting surfaces which, as in thesystem of the copending application, are almost planar, i.e., theirradii of cutvature r are greater than 10] and their individual powersArt/r are less than 0.11%. In contradistinction to the prior system, inwhich also the rear surface of the movable, negative third component ofthis group is nearly plane, the system according to the presentimprovement has as its third component a lens of definite meniscus shapewhose rear surface has a positive refractive power greater than that ofthe cemented surface of the immediately preceding doublet but less thatof either surface of the fourth, fixed component which is designed as abiconvex lens. Thus, the radius of curvature of this surface should besubstantially shorter than that of the two confronting doublet surfacesbut longer than any other radius of curvature of the varifocal frontgroup.

I have found that a system of this description allows the variable firstand third air spaces of the front group, i.e., those between the firstand second and between the third and fourth components, to assumeminimum values considerably smaller than in the prior system in thelimiting positions of minimum and maximum overall focal length,respectively; moreover, the stroke length of the movable third componentis appreciably reduced. Both these factors contribute to the greatercompactness of my present system.

The invention will be described in greater detail with reference to theaccompanying drawing in which:

FIG. 1 illustrates an optical objective system embodying the invention;

FIG. 2 is a view similar to FIG. 1, showing a modification of thesystem; and

FIG. 3 is a pair of diagrams giving the law of motion of the movablecomponents of the varifocal front group throughout the varifocal rangefor the system of FIG. 1 and FIG. 2 respectively.

The objectives shown in FIGS. 1 and 2 differ from each other only in themagnitude of certain parameters and are otherwise structurallyidentical. For this reason, the same reference characters have been usedin both instances.

In each of these objectives, a varifocal attachment or front group isconstituted by four air-spaced components I-IV, preceding a basicobjective or fixed rear group VI; between these two groups, an afocalcomponent V in the form of a reflex prism P is inserted; as in thesystem of the copending application, a diaphragm (not shown) may bepositioned next to this prism.

Component I is a doublet composed of a positive lens L with radii r rand thickness 11;, which is cemented onto a negative lens L having radiir r and thickness d components II, separated from component I by avariable air space d is likewise a doublet consisting of a positive lensL; (with radii r 1' and thickness d and a negative lens L; (with radii rr and thickness d cemented to it. Another variable air space dintervenes between this movable member and the next likewise movablecomponent III which is a single lens L with radii r r and thickness d,.The last component IV of the attachment, which follows component III bya further variable air space d is a positive singlet L with radii r rand thickness d,,. The large air space between the attachment I-IV andthe principal objective V1 is partly occupied by the prism P (componentV) of axial width (1 1, which is bounded by flat surfaces designated rand r separated from lens L, by a small air space d and from the fixedlens group VI by a larger air space d adapted to'accommodate thediaphragm. The basic objective VI consists of four air-spaced singletsincluding a positive lens L; with radii r r and thickness d anotherpositive lens L (radii r15, '1 and thickness 11 separated from the lensL; by an air space d a negative third lens L with radii r r and arelatively great axial thickness d17, this lens being separated fromlens L by the air space d and finally a positive fourth lens L (radii rr and thickness d whose separation d from the preceding lens L is lessthan half the thickness d of the latter.

The following Table I lists representative values for the radii r to rand the thicknessesand separations d to d g of lenses L to L (based upona numerical value of 100 for the mean focal length of the system), therefractive indices n of these lenses, their Abb numbers 11 and theirsurface powers An/ r, the system so defined having an aperture ratio of111.8, a back-focal length of 58.1 and a varifocal range from 55 to 210units (e.g., millimeters).

4 g ib-321.77 in f 101.39

For the minimum, median and maxium values of the overall focal length f,the variable air spaces d d and d have the following widths:

f (13 (lg (lg fmin---- 55 2.81 107.49 41.30 In 100 110.30 76.48 43.91jam... 210 224.45 15.24 4.50

If the prism P were removed, the air space TABLE I Thieknesses LensRadii an m u A n/r Separations n =+297.18 +0. 00207860 L d1 50. 00 1.61772 49. 78 I r2= 383.63 0. 00037557 L: dz 12. 50 1. 76180 26.08

d; 2. 81-224. 45 air space (variable) 1312.50 0. 00058042 L; d4 21.88 1. 76180 26. 98 II r -185.31 +0. 00074906 Li ds 6. 1. 62299 58.12

ra=+113.19 O. 00550303 d9 =197. -13. 24 air space (variable) r1= 146.62O. 00422889 III L d 6. 25 1. 62004 36. 34

d 41.89-4. air space (variable) rn= +200.56 +0. 00179016 IV Ls dn 12.50 1. 52015 63. 59

dm= 3. 13 air space T11= on V P dn= 56. 25 1. 51680 64. 20

T|2= ea d1:= 18. 04 air space m= +124.00 +0. 00546603 L d1;= 13. 1.67700 55. 52

d 0. 25 air space 1 =+56.31 +0. 01237435 L; d 14. 87 1. 60680 55. 61

rn= +8550 0. 00814070 \-'I d1e= 7. 50 air space m= --177.50 O. 00442084La dn= 19. 68 1.78470 26. 10

d 8. 12 air space T1q= +13.00 +0. 00800000 L10 (in 14. 38 1. 74400 44.

tota\ 44 The individual focal lengths of the components I, II, III, IVand VI of the foregoing system have the following numerical values:

following Table II and illustrated in FIG. 2, has a backfocal lengths=72.27 representing a considerably increased ratio s'/d its overallfocal length 1 being variable from 57 to 215 units and its relativeaperture being 7 again 1:1.8.

TABLE II Thlcknesses Lens Radil and m w A n/r Separations r +2641? +0.00233834 1., (I; 44. 44 1. 61772 49. 78 I r2= 84l .00 0. 00042252 11; 2.50-199. 50 air space (variable) n= 1166.67 0. 00065297 L; d4 19. 441.76180 26. 98 II r5= 164.72 +0. 00084270 115 =175. 56-11. 78 air space(variable) r1= 130.33 0. 00475746 III L5 d1 5. 55 1. 62004 36. 34

(is 37. 22-4. air space (variable) rn=+258.28 +0. 00201389 IV L do 11.111.52015 63. 59

d 19.44 air space T11= m V P d11= 50.00 1.51680 64.

T1i= co du= 24. 44 air space m=+143.44 +0. 00487876 L1 dia= 11. 39 1.69981 34. 69

d14= 0.28 air space n5= +57 .94 +0. 01207076 Lg (1 12. 22 1. 69938 49.74

ne=+07 .11 0. 00720193 VI d 6. 94 air space m= --185.89 0. 00433148 L9di7= 11. 04 1. 80518 25. 46

d1g= 8. 33 air space m= +15.89 +0. 00764938 L d r= 29. 44 1. 73350 51.04

The magnitudes of the three variable air spaces in the principalpositions of adjustment are as follows:

f s o da fInin--.. 57 2.50 175.56 37.22 100 101.52 72.57 41.10 1...--.215 199.50 11.78 4.00

Upon a progressive change in the first air space d by an axialdisplacement of component II, component III should undergo acompensatory displacement with consequent changes in air spaces 11,, andd as shown graphically in FIG. 3. Each diagram (a) and (b) of thisfigure, respectively relating to the system of FIG. 1 (Table I) and tothat of FIG. 2 (Table II), has a graph showing the variation of airspace d; and another graph representing the sum of air spaces d d as afunction of overall focal length f. Naturally, the sum of the three airspaces d d and d must always remain constant, constituting as it doesthe separation of the fixed components I, IV diminished by thethicknesses of components II and III.

From the listed values of the individual focal lengths of the severalcomponents it will be noted that, in each of the two systems disclosed,the absolute value of the individual focal length of component II isless than that of any other component of the front group and less thantwice that of the basic objective VI, being thus also less than theupper limiting value f -2f -2f of the system.

Although the front component II has been referred to as fixed, it is tobe noted that, for focusing purposes, this component may be limitedlyaxially displaceable in the well-known manner. I

I claim: a

1. An optical objective system comprising a variable front group and afixed basic objective, the system having an overall focal lengthvariable between a minimum value f and a maximum value f respectivelysmaller and larger than the individual focal length of said basicobjective, said front group consisting of an at most limitedlyadjustable positive first component on the object side of the system, anaxially movable negative second component following said firstcomponent, an axially movable negative third component following saidsecond component and a fixed positive fourth component following saidthird component and facing said basic objective, said first componentbeing a doublet with a convex forward face and a negatively refractingforwardly concave cemented surface, said third component being ameniscus-shaped singlet with a convex rear surface, said fourthcomponent being a biconvex singlet, said doublets being provided withnearly planar confronting surfaces, said rear surface of said thirdcomponent having a positive refractive power greater than that of thecemented surface of said second component but less than that of eachsurface of said fourth component; the lenses L L of said firstcomponent, the lenses L L, of said second component, said thirdcomponent L and'said fourth component L having radii r to r andthicknesses and separations a, to d whose numerical values, based upon anumerical value of for f.,, along with the refractive indices n and theAbb numbers 11 thereof are substantially as given in the followingtable:

Thicknesses Leas Radii and m Separations r +297.18 L1 (lr=50.00 1. 6177249. 78

r:= 883.63 In tl:=12.50 1. 76150 26. 98

=2.81'224.45 air space (variable) r4= 1312.50 La d4= 21.88 1. 76180 26.08

r 185.31 L4 d5= 6.25 1. 62290 58. 12

(ls=1J7.4J13.24 air space (variable) 17 146.62 L d 6.25 1. 62004 36. 34

d =41.89-4.50 air Space (variable) r =+200.56 La d 12.50 1.52015 63. 59

2. A system as defined in claim 1 wherein said basic objective consistsof four air-spaced lenses L L L L whose radii r to r thicknesses andseparations d to (1 refractive indices n and Abb numbers 1/ aresubstantially as given in the following table:

3. An optical objective system comprising a variable front group and afixed basic objective, the system having an overall focal lengthvariable between a minimum value f and a maximum value j respectivelysmaller and larger than the individual focal length of said basicobjective, said front group consisting of an at most limitedlyadjustable positive first component on the object side of the system, anaxially movable negative second component following said firstcomponent, an axially movable negative third component following saidsecond component and a fixed positive fourth component following saidthird component and facing said basic objective, said first componentbeing a doublet with a convex forward face and a negatively refractingforwardly concave cemented surface, said third component being ameniscus-shaped singlet with aconvex rear surface, said fourth componentbeing a biconvex singlet, said doublets being provided with nearlyplanar confronting surfaces, said rear surface of said third componenthaving a positive refractive power greater than that of the cementedsurface of said second 8 component but less than that of each surface ofsaid fourth component; the lenses L L of said first component, thelenses L L; of said second component, said third component L and saidfourth component L having radii r to r and thicknesses and separations dto d whose numerical values, based upon a numerical value of for f alongwith the refractive indices n and the Abb numbers 11 thereof aresubstantially as given in the following table:

Thickucsscs Lcus Ratlii and M v Separations dz= 11.11 1.76180 26. 98 r3055.55

(1 :2.50-10950 air space (variable) 1 1166.67 L; d 10.44 1. 76180 26. 08

T 164.72 L d 5.55 1. 62299 58. 12

d =175.5611.78 air space (variable) T1= -130.33 L d1=5.55 1. 62004 36.34

d@=37.22-4.00 air space (variable) r +25828 Lu do=11.11 1. 52015 63.59

4. A system as defined in claim 3 wherein said basic objective consistsof four air-spaced lenses L L L L whose radii r to r thicknesses andseparations d to d refractive indices n and Abb numbers I! aresubstantially as given in the following table:

JOHN K. CORBIN, Primary Examiner US. or. X.R. 3so 202, 214, 223

